Humidity control



Sept. 21, 1943. Q E, JOHNSQN 2,329,908

HUMIDITY CONTROL Filed July 28. 1959 v giu/11014430@ Patented sept. 21,1943 2,329,908 nUMmIrY CONTROL Cecil E. Johnson, New York, N. Y.,

rm Reddir, Inc., Application July 28,v 1939, Serial No. 287,165 1 Claim.(Cl. S12-31) This invention is directed to the packaging of articles sothat they are maintained with a proper moisture content.

It is well recognized that many articles should be specially packaged tokeep them from either drying out or absorbing too much moisture, astheir moisture content determines their freshness. Such articles are,for example, tobaccos, candies, chewing gum, photo illms, and otherperishable goods. A common manner yofmaintaining the moisture content ofsuch articles is ,by packaging them in hermetically sealed containers.Obviously the water content does not vary but minutely within ahermetically sealed package and the problem of maintaining the"freshness of packaged articles is effectively solved. The expense ofthis method of packaging, however, prevents its use With low costarticles, and particularly articles which'have a relatively short lifefrom the manufacture to the consumption thereof. Other methods have beensuggested, as by packaging the articles together with some substancewhich will yield water, and to some extent take up "water, from thearticle on changes of the humidity within the package. For example,sponges soaked in water have been inserted into humidors containingtobacco; Glaubers salt has been inserted into containers of tobacco;solutions adapted to maintain a substantially constant vapor pressureehave been placed in containers sch as bread boxes for the purpose ofmaintaining the humidity of the container constant; and articles havebeen packaged within protective layers of the same article in order thatthe packaged innermost article may retain its original moisture content.

4With the exception of sealing articles in hermetically sealedcontainers, and surrounding an article with similar articles, the othermethods of packaging articles for the purpose of keeping their watercontent substantially constant have all been impractical as they failedto account for more than the continual leakage of water 'from thepackage. This leakage has been recognized'as actual, but hitherto knownmethods, beyond supplying loosely attached water in some form to make upthe leakage, have failed to recognize the more important factor ofcontrol in the amount of water supplied to make up that lost by leakage.The vapor pressure created by the water present in the packaged articlewill vary with change in temperature. The humidifying element whichsupplies the water lost by leakage should function at all times in amanner to keep the article in the package surrounded by assigner to thei Wilmington, Del.

a Water vapor pressure just equal to that which the packaged articlewould create by itself under any temperature condition if .the articlewere sealed in a water impervious container. Under ideal conditions thecontrol should be in that the water in the packaged article is inequilibl rium with the water vapor pressure of the humidifying elementand there is no permanent water loss from the article, but only an.equilibrium exchange. This condition must be met for all temperaturesto which the packaged article is to be exposed, and must be in eiect apractical means of paralleling the water vaporpressure of the wrappedarticle, when said article is packaged in an ideal container. Waterlvapor pressure as herein discussed may be expressed in terms of relativehumidity, which is the quotient of the partial pressure of water vaporat any temperature, divided by the partial pressure of saturated vaporat that temperature. Therefore relative humidity is the percentage/vaporpressure and it is more common to speak in terms of relative humiditythan in terms of vapor pressure.

Glaubers salt has previously been used as a humidifying element forpackaged articles. 'I'his hydrated salt will serve as an example of anuncontrolled water supply. Thus, Glaubers salt has a relative humidityalways over at most normal temperatures less than approximately F.However, if the temperature rises above 80 F., the relative humidityproduced by the Glaubers salt will go up proportionately to become aboutat 90 F. Consequently, if an article is packaged with a relativehumidity of, for example, 70%, Glaubers salt added to the package willnot maintain that same humidity over a substantial temperature range.Again, Glaubers salt will not produce a relative humidity less than 70%.The use of this salt failsy to control the quantity of water in thepackage in order to maintain a constant humidity. The variation given byand the lack of control from a water soaked sponge is even greater asthe water vapor emitted from the soaked sponge gives a. relativehumidity of approximately at most normal atmospheric temperatures.Consequently a water soaked sponge cannot be used to maintain a humidityof, for example, 70% over the normal atmospheric temperature range. Thusthese substances are not satisfactory when used in a moisture tightcontainer, and much less satisfactory when used in a moisture perviouspackage.

A further objection to the prior art attempts to maintain asubstantially constant water content in a packaged article lies in thefact that the water content for most articles must be maintained withina very limited range, and the prior art substances were incapable ofmaintaining the humidity within the necessary limits at least during theusable life of the article. Except for hermetically sealed containers,the perviousness of the ordinary package to the ingress and egress ofmoisture prevents the mere addition of wetting or drying substances tothe package from being sufficient to compensate for atmospheric changeswhich affect the condition of the articles within the package.Consequently the additional water conditioning substances are influencedmore by atmospheric conditions than by the changes in the condition ofthe articles purportedly protected, with the result that the additionalsubstances are practically useless.

Still another objection lay in the fact that the A insertion of a wetsponge or other moisture conditining substances into a package, or thepackaging of an article within like articles, gave weight, bulk, andadded cost without producing such advantages as would compensate for therather ineiective moisture control in the package.

An object of this invention is to provide a substance which can bepackaged with an article to maintain a substantially constant absolutewater content in the article to be packaged.

Another object of the invention is to package articles with a particularsubstance which can be modified by additional substances so that changesof the vapor tension within the package are compensated by the substancein such a manner as to keep the absolute water content of the articlessubstantially constant.

Another object of the invention is to utilize a substance which is notonly a humidifying agent, but also an adhesive agent so that it can beused as the adhesive in assembling the package which is to contain thearticle to be humidied.

Another object of the invention is to surround packaged articles with anwrapper including a substance which inherently maintains over a widetemperature range the same humidity as that of the article at the timeof packing, the substance preventing the article from being affected byconditions outside the package both by acting as a barrier between thearticle and outside conditions and by compensating for changes withinthe package which would ordinarily cause a change in the moisturecontent of the article.

Another object of the invention is to employ an adhesive humidifyingsubstance of low cost which is non-toxic and usable with comestibles.

Another object of the invention is to employ a humidifying substancewhich will maintain the humidity of a packaged article within Very closelimits during the market life of the packaged article.

Another object of the invention is to construct a laminated sheetproduct including an adhesive layer of specific humidifying propertiesand at least one moisture pervious layer.

Generally these objects of the invention are accomplished by enclosingan article whose absolute water content is to be maintainedsubstantially constant with a humidifying device including a substanceof high molecular weight, sticky, water soluble, non-volatile, andnon-toxic. Such a substance can be composed of a compound of invertsugar or heavy sugar solution which .may be modlned by the addition ofone or more substances in order to produce a substance which has thesame humidity at all temperatures as the humidity of the article at thetime it is packaged,

\- or, in other words, a substantially unvarying relative humidity. Theadded substances may be sucrose and glycerine. Starch and talc and thelike may be added in order to control the viscosity of the finishedsubstance. Such a substance has the advantage of being adhesive so thatit can be used to construct a package, and further is non-toxic andinexpensive. The water content of the substance is such that it canrelease a reasonable amount of water into the package withoutsubstantially changing its own normally maintained humidity, andconversely it can take up a reasonable quantity of water withoutsubstantially varying its humidity. This material thus functions tocontrol the quantity of water in a package for changes in vapor pressureover a normal atmospheric temperature range of about from 32 F. to 110F.

These and other objects of the invention may be more readily understoodby reference to the following specification, taken in connection with Athe drawing, in which:

Fig. l is a perspective view of a portion of a laminated sheet ofmaterial embodying the invention.

Fig. 2 is a similar view showing the use of a sheet of crinkled paper.

Fig. 3 is a. perspective view of a cigarette package, with the layers ofthe package cut away to show the manner of using the invention.

Fig. 4 is a plan View of a sheet of material showing how the adhesivemay be applied thereto.

Fig. 5 is a cross sectional view of a tin can containing, for example,cigarettes, showing the use of the invention therein; and

Fig. 6 is a cross sectional view of a box, as a candy box, showing theapplication of the invention thereto.

In Fig. 1, a laminated structure is shown comprising two sheets ofmaterial 2 and 4 adhesively united by a layer 6. This adhesive layer iscomposed of an invert sugar solution modied to produce a desiredhumidity which is constant for all normal atmospheric temperatures. Inother words, the adhesive is given the property of changing its vaporpressure at a rate which maintains a constant humidity which is the samefor the packed article. For Iexample, an adhesive composition which willproduce the 60% humidity desired in the packaging of cigarettes may haveone of the following compositions:

Example A Grams '15% aqueous solution of invert sugar-- 200 Sucrose 27Water 5 Starch 5 Total weight 237 231 Example B Grams 75% aqueoussolution of invert sugar 200 Sucrose 0 Water 5 Starch 5 Total Weight 230229 Glycerine` 10 239 Example C' In preparing these compositionsthestarch is mixed with the water; the sucrose and invert sugar are warmedtogether to form a clear solution, these two substances being moresoluble when used together than when dissolved separately; the invertsugar-sucrose solution is then stirred into the starch-water mixture;the entire mixture is then heated to bulk the starch and to remove wateruntil the total weight in Example A is dropped to 231 grams, and inExample B to 299 grams. In`Example B, glycerine is added but thisaddition is made preferably after the solution is cooled. The adhesiveobtained in Example A is relatively viscous. The

adhesive obtained in Example B is relatively thin,

the thinning being eiected by reducing the.

amount of sucrose over that in the A formula and by the addition ofglycerine. The adhesive obtained in Example C has a viscosity which isthe ingredients. such variation being made in a manner that keeps thehumidity balance unchanged. A decrease in the sucrose content and theaddition of glycerine gives a method for decreasing viscosity. Higherviscosity may be obtained by a limited increase in the sucrose contentor by the use of additional starch.

In the above examples, the invert sugar consists of 75% solids and 25%water, i. e. 75 Brix. A representative such as sodium benzoate may beadded. The glycerine may be replaced by glycols such as ethylene glycol,or by inorganic lactates such as sodium lactate.

It has been demonstrated that the above compositions are extremelyadhesive, form a ilexible adhesive lm which is slow drying, and as amatter of fact, is substantially non-drying during the usable life ofthe wrapper, and are able to give up and take up water so that theymaintain a substantially constant relative humidity. Thus, assuming thatthe layers of sheet material 2 and 4 are composed of porous paper, theadhesive 6 will either release or take up water vapor through the poresof the sheets 2 and l in an eii'ort to maintain itself at itspredetermined relative humidity. It has been demonstrated by repeatedexperiments that the adhesive layer maintains its relative humiditywithin a narrow range approximating a 1% change even though the ambienttemperature undergoes a wide change, say, for example, from 35 F. to 105F. It is believed that the reason the relative humidity remains constantis because the adhesive automatically' maintains, in itself, a constantratio as to the dissolved solids and water. That is, when the adhesiveloses water, some of the solids will crystallize out, at a rate equal tothe loss of water, thereby maintaining a. constant ratio between thedissolved solids and the amount of water in the solution. Conversely, as

the adhesive absorbs water, the crystallized partlcles willl go backinto solution, thus maintaining the constant ratio. Regardless of thetheory of operation, many and repeated experiments have proved that anadhesive composed of properly t selected substances and compounded asdescribed has a. substantially unvarying humidity over a widetemperature range.

It is not necessary that both the layers 2 and 4 be'of sheet materialpervious to the passage of water vapor. As a matter of fact, itispreferable to have one of the layers, for example, the layer 2, composedof a layer impervious to water vapor so that the sheet material can beused as a package with the layer 4 innermost. Such impervious sheetmaterial can be metal foil or waxed paper. The very tacky and slowlydrying characteristics of this humidifying adhesive make it very easilyapplied and spread over sheets 2 and 4. It has a special advantage when'used with metal foil in that it firmly unites all portions of the metalfoil to the other layer, and thus provides an excellent reinforcingmeans for the foil.

In Fig. 2, the sheet 2 with the adhesive layer 6 is again shown. butinstead of using a plain sheet of paper, a crinkled sheet of paper, forexample, crepe paper, is used to form the layer 8. This allows the useof more adhesive 6 without appreciably thickening the laminatedmaterial. Y

The application of this novel laminated material to the packaging ofcigarettes is illustrated in Fig. 3. It is first of all noted that thetobacco in cigarettes is very sensitive to changes in moisture, and thata fresh cigarette has an absolute moisture content of almost exactlyv12% water. This corresponds to a relative humidity of approximately 60%in the package. A variation of 1% in the moisture content ofthecigarettes causing a drop to 11.00% or an increase to 13.00% will eithermake the cigarettes too dry or too wet. A variation of 0.5% ispermissible and therefore it is essential tomaintain the cigarettes witha water content ranging between 11.50% to 12.50%. In explanation, aWater content of 11.50% corresponds to a relative humidity of- 58%, anda water. content of 12.50% corresponds to a relative humidity of 62%.Thus, any humidifying substance added to the package should maintain therelative humidity of the package between the limits of 58% and 62% overa normal atmospheric temperature range, and for the marketing life ofthe package. Of course, the humidifying substance must be in such formthat it does not stainthe cigarette, is not toxic, and is inexpensive.

The adhesive and the manner of using it as disclosed in this inventionsatisfy the above conditions. Thus, in Fig. 3, the cigarette package isshown having the conventional outer Cellophane Wrapper I0, and the innerpaper wrapping material I2. The innermost wrapping material comprises alaminated structure formed of metal foil I4, an adhesive layer I6, andan inner layer of paper I8. The layers I4, I6 andv I8 form a laminatedproduct substantially as described for either Figs. 1 or 2. The adhesivedescribed satisfies the conditions for maintaining the cigarettes in thepackage within the desired limits of 11.50% to 12.50% water content overthe normal atmospheric temperature range. Asa matter of fact, theadhesive substance has the same vapor pressures at differenttemperatures as would exist for the cigarettes if the absolute watercontent of the cigarettes remained unchanged over a temv perature range,and thus will maintain the relative humidity of the package within a 1%variance from the 60% relative humidity corresponding to the 12% watercontent of the cigarettes. In other words, the adhesive mixtures givenin the above examples, more than satisfy the necessary conditions forthe proper packaging of cigarettes. Inasmuch as in the usual cigarettepackage, the layers I4 and I8 are normally secured together by adhesive,the adhesive layer I6 performs the ordinary function of securing thelayers I4 and I8 together, and therefore the making of such does notnecessitate any change in the packaging machinery. However, the layer I6produces the unobvious result in that the adhesive substance can eithertake on or give up moisture to the cigarettes in order to maintain thecigarettes at their desired water content. If one and one-half grams ofthe adhesive in Example A is used as layer I6, it will hold 0.33 gram ofwater. This water content can be lowered or raised appreciably withoutmarked effect on the humidity balance and since the extreme loss or gainfrom twenty cigarettes generally does not exceed 0.17 gram of water frommanufacturer to consumer, the layer I6 oiers adequate protection. Thelayer I6 has the further function in that it acts in the nature of aseal against water vapor which might possibly escape through the metalfoil I6, and at the same time it constitutes a reservoir of water forthe package.

In Fig. 4, the adhesive layer 20 is shown applied to the sheet material22 spaced from the margins thereof. Figs. l and 2 indicate that theadhesive is spread uniformly over the entire surfaces of the sheets.However, as the adhesive might ooze out from between the sheets when thesame are folded into package form, and thus come in contact withcigarettes or other packaged articles and thus stain them, it isdesirable to keep the adhesive within the outer edges of the layers ofsheet material. This is readily done by spacing the adhesive 20 from theedges of the sheet material 22, as shown in Fig. 4. The only necessaryqualification is that su'lcient adhesive be added to the package so thatthe adhesive can influence and control the humidity of the package.

In Fig. 5, a can 30 is shown having a cap 32 and enclosing cigarettes34. To the inner face of this cap is applied a layer of the humidifyingadhesive 36 having a composition similar to those previously describedand being covered by a layer of moisture pervious paper 38. In effect, alaminated humidifying device is achieved by the layers formed from thecan, the adhesive, and the paper in accordance with the teachings ofthis invention, hence the adhesive layer could be applied to the side orto the bottom walls of the can, or the entire interior of the can. Itcan be seen that the laminated humidifying device can be made to conformto the shapeof the container. As the can 30 is of metal, it is notnecessary to use an impervious metal foil layer. lHowever, if thepackage were cardboard, the entire inner during a normal six weeksperiod contents of the package or a part thereof, could be covered byusing a laminated sheet such as shown in Figs. 1 and 2.

Fig. 6 demonstrates a possible use of the humidifying device of theinvention in a candy box 40 having a top 42. Sheets of soft paper 44simllar to the rather fluffy sheets used in candy boxes and united bythe humidifying adhesive to form a laminated structure as shown in Figs.1 and 2. are inserted above, below, and between the layers of candy. Ifdesired, the upper and lower sheets could have their surfaces toward thewalls of the box formed of metal foil, or other impervious material,thus reducing leakage of water vapor from the box.

It ls to be understood that the invention is capable of many differentapplications, and only a few of the applications have been given merelyfor the purpose of illustrating some of the uses. rI'he importantfeature of the invention resides in the fact that the article to bepackaged, be it cigars, cigarettes, chewing gum, photo film, etc., canbe packaged at its preferred humidity, with the humidifying devicehaving the same preferred humidity and incorporated in the package,either as a wrapper as in Fig. 3, in the form of a laminated structureas shown in Fig. 6, or as a structural part of the package as shown inFig. 5. The separation of the adhesive from the contents of the packageby a water pervious layer keeps the contents of the package from beingstained or stuck by the adhesive. The modified invert sugar solutionsused are remarkably invariable in their vapor pressure over a widetemperature range and when properly incorporated within a packageconstitute an accurate, inexpensive means of maintaining a desiredhumidity around packaged articles.

Broadly, the inventive improvement over the prior art lies in thecreation of a humidifying device wherein a humidifying adhesive is fixedto a vehicle so that it can be used to protect an article withoutencumbering or changing the properties of the article. The humidifyingdevice not only has the same vapor pressure as the article at the timeof packaging, but practically parallels the various vapor pressurestaken at different temperatures by the article if the absolute watercontent of the article remains substantially unchanged, and thehumidifying device is as temperature sensitive as the article.

Having now described a means by which the objects of this invention maybe obtained, what I claim as new and desire to secure by Letters Patentis:

A non-hermetically sealed package comprising a moisture-bearing articlehaving a definite vapor pressure and a wrapper, at least a portion ofthe wrapper comprising an outer layer of substantiallymoisture-impervious material, an intermediate layer of liquidwater-bearingadhesive material, and an inner layer of moisture-perviousmaterial; said intermediate material comprising a liquid water-bearing,slow drying, hygroscopic plastic including a reservoir of water andhaving a. vapor pressure substantially equal to that of themoisture-bearing article, said liquid water in said plastic being in anamount sulcient to replace into said article at a vapor pressurecorresponding to the initial vapor pressure of said article water lostfrom said article over a time period corresponding to the normalmarketing life of said package.

CECll. E. JOHNSON.

